Hello All
I completed the construction yesterday.
http://ad2004.hku.nl/naturesound/TomR/PRHSB/wired%20up.JPG
shows the focal point capsule array and the parallel boundary
arrangement (a la Curt Olsen) mounted in the reflector and wired up.
You might note the capsules do not have the powering arrangements
mounted on their strip boards. The power supplies have been put in a
separate box and mounted on the handle of the reflector.
http://ad2004.hku.nl/naturesound/TomR/PRHSB/capsule%20power+control.JPG
shows the power and potentiometer boxes on the handle. Lots of wires
looking like a bit like a rats nest I'm afraid but a decent bit of
PCB design would make it all much more streamlined.
Today has been a perfect weather day - shirt sleeve temperatures and
no wind in the middle of February! A great day for the first test of
the Parabolic Reflector with the Head Spaced Parallel Boundary - PRHSPB.
http://ad2004.hku.nl/naturesound/TomR/PRHSB/PRHSB%20Test%20Range.jpg
shows the test range. Most important - note the small radio mounted
about 6 feet up the trunk of the willow tree. This has the facility
of producing "white noise" as an option in its sleep mode (anyone
found sleeping during the following tests will be reprimanded :-) The
reflector was aimed at the radio which was 40 feet away. The volume
of the radio was set such that I could barely hear it when standing
next to the reflector. However, the bird bath fountain, to the right
of the reflector, was easily heard.
The test was to alternate between the extremes of the potentiometer
settings i.e. maximum output from the parallel boundary capsule array
( focal point capsules at minimum) to maximum output from the focal
point array (boundary capsules at minimum )whilst keeping the
reflector pointed at the radio. I was standing behind the reflector.
After turning the potentiometer knob I announced the capsule arrays
that had maximum output.
Here is a section of the recording with the sounds of the
potentiometer being turned and my announcements edited out. There are
two segments of focal point capsules at max. and two with the boundary
capsules at max; no prizes for guessing which is which.
http://ad2004.hku.nl/naturesound/TomR/PRHSB/Edited%20Selected%20Portion%20mp3.mp3
Here are the same recorded segments with my announcements and the
sounds of the potentiometers being operated. Its not necessary to
listen to these if you don't want to.
http://ad2004.hku.nl/naturesound/TomR/PRHSB/Selected%20Portion%20mp3.mp3
Finally here is a three segment (each of 20 seconds) recording with a)
the boundary capsules at max, b) the potentiometer mid way between the
boundary and focal point, and c) the focal point capsules at max.
http://ad2004.hku.nl/naturesound/TomR/PRHSB/Three%20Section%20mp3.mp3
For the record the relevant recording information is:-
Sony MZ-RH910 HiMD recorder, with manual volume control set at 18.
The boundary capsules were 4 inches in front of the focal point
capsules. The boundary capsules were 1 inch in front of the plane of
the rim of the reflector and were 2 inches away from the front of the
parallell plates of the boundary arrangement.
To my ears there is no doubt that the test was successful in proving
that the concept works. There is plenty of fine tuning to be done
such as varying the distance between the focal point and boundary
capsules, the distance of the boundary capsules from the front of the
plates they are mounted on, and the distance the boundary capsules are
above the reflector rim. The inherent low quality of the Rapid
capsules are also an issue that might be improved on.
Another point I'm not sure of is how such a system would be used in
the field. Would one use it like a normal parabolic to get a species
recording and then zoom out to obtain a better picture of the setting
in which the recording was made? Or, vice versa, zoom in on a
particularly interesting sound within a wider stage. Probably both I
imagine.
Cheers
Tom Robinson
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